Not applicable.
The present invention relates generally to the deposition of a film using plasma polymerization, and in particular, to a deposition wherein a poled polymer material is formed by applying a poling field during the plasma polymerization process.
Nonlinear optical devices formed from poled polymer materials are used in numerous applications, such as planar waveguide modulators or second harmonic generators in integrated circuits. Typically the poled polymer material is fabricated by poling a polymer film after the film has been formed. For example, a polymer film containing chromophores with high polarizabilities can be heated to near its glass transition temperature and subjected to an electrostatic field (poled power supply) to align the chromophores based upon their dipole moments. When the polymer film is cooled, the molecules are captured (frozen) in the oriented (poled) position. While this is a straightforward process, there are disadvantages. One significant disadvantage is the gradual relaxation of the oriented position over time, and hence, instability in the nonlinear characteristics of the film. Another disadvantage is the multi-step process of: forming the polymer material; thermal cycling the material to near glass transition temperature; applying a relatively large electrostatic poling field to the material; and bringing the polymer material back to room temperature. Therefore there is the need for a poled polymer material that can be formed in a single stage process while exhibiting an extended temporal stability.
In one aspect, the present invention is an apparatus for and method of depositing a poled plasma film on a substrate in a substantially air-tight chamber. The substrate is disposed between a positive plasma-generating electrode and a ground electrode that are connected to a plasma excitation power source. Poling electrodes are provided in the chamber and connected to a de voltage source so that a nonlinear optical reactant that is injected into the chamber can be poled as the plasma generated from the reactant induces polymerization and initiates a deposition onto a surface of the substrate to produce a poled polymer film on the substrate in the region of the electrostatic field established by the dc voltage.
The poling electrodes may be arranged in alternative configurations within the chamber. Positive and negative poling electrodes may be arranged in contact with the surface of the substrate and the poled plasma deposition on the substrate may be accomplished within a gap between the poling electrodes. In another arrangement, the positive and negative poling electrodes are arranged with a gap between them in the vicinity of the substrate""s surface that opposes the deposition surface of the substrate. The electrostatic field established by the de voltage penetrates through the substrate and into the deposition region of the surface. In another arrangement, the positive poling electrode is disposed in the vicinity of the surface of the substrate facing away from the ground electrode, and the ground electrode serves as the negative poling electrode. In this arrangement, the poled plasma deposition takes place on the surface of the substrate facing the ground electrode.
These and other aspects of the invention are set forth in the specification and appended claims.